In Patent Literature 1, there is disclosed a network system in which the load imposed on a Web server(s) within a site is alleviated by a load balancer to enable high-speed path switching even on occurrence of failures on a path getting to the load balancer. According to Patent Literature 1, when a router disposed halfway between a client terminal and a server has received a packet from the client terminal, the router decides on a forwarding destination server based on a destination L4 port number as well as a hash value of a source address contained in a packet header. By so doing, it is possible to allocate processing to servers that differ from one service recognizable on the layer 4 (L4) to another.
In Patent Literature 2, there is disclosed a load balancer which will prevent deterioration of a response characteristic to the client terminal as uniqueness is positively maintained. In this Patent Literature, a relay apparatus(es) arranged between the load balancer and the server references a response from the server to the client terminal to post-write or add a path identifier (an identifier allocated from one relay apparatus to another) in L7 data. When the client terminal re-sends the request, the path identifier, received last time, is embedded in the request. The load balancer that has received the packet transfers it to an appropriate one of the relay apparatuses.
In Patent Literature 3, there is disclosed a computer system in which the processing of deciding a forwarding destination is divisionally taken charge of by a plurality of apparatuses so as to reduce the storage capacity or the amount of calculations of a URL (Uniform Resource Locator) switch.
In Non-Patent Literatures 1 and 2, there is disclosed a centralized control type network called an OpenFlow exploiting a centralized control configuration network architecture in which a control apparatus termed an OpenFlow controller controls the behavior of a switch termed an OpenFlow switch. The behavior of a number of these switches, making up a virtual network, can be flexibly modified in keeping with the status of the entire network. Thus, with the use of the OpenFlow, a highly flexible virtual network can be constructed with much ease.
Patent Literature 1:
    JP Patent Kokai Publication No. JP2003-131961APatent Literature 2:    JP Patent Kokai Publication No. JP2011-041006APatent Literature 3:    JP Patent Kokai Publication No. JP2006-309383ANon-Patent Literature 1:    Nick McKeown and seven others: “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Feb. 14, 2012], Internet <URL: http://www.openflow.org/documents/openflow-wp-latest.pdf>.Non-Patent Literature 2:    “OpenFlow Switch Specification, Version 1.1.0, Implemented (Wire Protocol 0x02),” [online], [searched on Feb. 14, 2012], Internet <URL: http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>.